This invention relates generally to aerial vehicles, and relates with particularity to supersonic aircraft having excellent subsonic flight capabilities and utilizing a variable dihedral tail unit to vary the aircraft geometry.
One of the major problems for the design of supersonic aircraft is the variation of center of lift with Mach number. The variation generally encountered consists of a rearward shift in center of lift in going from subsonic to supersonic speeds with an attendant increased trim drag. The significant factor contributing to this change in center of lift is the rearward shift of wing center of pressure.
For low speed flight, and for takeoff and landing, it is desirable that there be horizontal tail surfaces to take maximum advantage of the tail moment arm in providing stability and control. However, for supersonic flight, the horizontal tails increase drag and are unnecessary if the aircraft center of gravity is aligned with the supersonic center of lift.
To compensate for the wing center of pressure shift, the current practice is to shift fuel to reposition the center of gravity of the aircraft. This requires installation of a separate fuel transfer system in the aircraft to pump a massive amount of fuel either forward or aft as required. This system, which is normally used only when traversing through the Mach 1 region, is inefficient, quite costly, and requires excess fuel capacity. An alternate approach has been to use retractable canard surfaces. However, this adds extra surfaces and the control mechanisms therefor which increase weight and drag, especially during supersonic flight.